An assembled battery module uses a plurality of assembled batteries. Each assembled battery comprises a plurality of batteries and assembled battery monitoring circuits. The monitoring circuit of each assembled battery is powered by the batteries composing the assembled battery.
When the assembled batteries are connected in series, that is, the monitoring circuits of the assembled batteries are connected in series through a communication line, the monitoring circuit of the assembled battery communicates with the other monitoring circuits of the other assembled batteries with a large potential difference. This causes a problem in the possibility and stability of communication.
In the prior art, as a method of communication under conditions generating a large potential difference, it is known to isolate a reference potential of each circuit by using an isolation transformer or optical isolator.
Generally, a large current is necessary for a circuit which makes communication in an isolated state by using an isolation transformer or optical isolator. Thus, if such a circuit which makes communication in an isolated state is used in a monitoring circuit of an assembled battery, power may be wasted, and the power storing performance of an assembled battery module may be decreased.
Besides, when an assembled battery module is actually used, the communication stability is demanded even for noise from an inverter or converter.
Therefore, there are technical needs to ensure stable communication even for a state with a large difference between the reference potentials of communicating circuits.